The present invention relates to a control circuit for electric motors, such as direct current motors which drive electrical vehicle, such as golf carts, fork lift and the like but may be used for any electrical drive.
The prior art reveals several attempts to provide control circuits for controlling current supply for direct current motors. For example, U.S. Pat. No. 3,517,290 discloses thyristor control circuit, particularly for electrical vehicles, such as small tractors, fork lift trucks. The power circuit of a motor is supplied intermittently with power through a thyristor. Such circuit, however, has drawbacks that the ripple factor of current through the power circuit is not constant. Further, the operability that is the duty (which may also be called ON-OFF ratio or mark-to-space ratio) against the amount of depression of an acceleration pedal, is unstable and can be easily affected by change in the output of battery.
Other prior art which are relevant to the present invention are as follows:
(1) Japanese Patent Laying-open No. 52-64714 (Mar. 28, 1977) "Control Circuit of Thyristor Chopper for Use in Electrical Car"; and PA1 (2) U.S. Pat. No. 3,517,292 (June 23, 1970) "Transistor Power Switching Circuit for Pulse Modulation System".